Our objective is to find out how stromal melanocytes of the rhesus eye grow and differentiate, how they interact with the non-pigment-forming cells of the uvea stroma and what their functions are. Anatomical and functional considerations suggest that stromal pigment cells have activities other than light screening yet to be defined. We have demonstrated that the fine structures of melanosomes in choroidal melanocytes undergo changes quantitatively and qualitatively correlated with increasing age. Their enzyme profile also changes with age. We have determined that choroidal melanocytes of adult eyes are nonreplicative differentiated cells, and that they depend on other cell types for survival in culture. We will study by electron microscopy and cytochemical techniques how the stromal pigment cells in culture interact when they are grown separately or together with various cell types of the stroma and how they respond to chemical or physical agents in the environment. Our study on their growth and differentiation in normal and abnormal states promises a better understanding of their roles in health and disease.